Prestressed reinforced concrete mast



Jan. 12, 1960 R. J. D. FINFROCK PRESTRESSED REINFORCED CONCRETE MASTFiled Dec. 27, 1955 Q5? 2 WA 2), VAINVENTOR 16 j 6 mase7zzafm fem,

v BY P L 72 7 ATTORNEY United! States Patet PRESTRESSED REINFORCEDCONCRETE MAST Robert J. D.'Finfrock, Orlando, Fla.

Application December 27, 1955, Serial No. 555,439

3 Claims. (Cl. 72-85) The present invention relates to a mast formed ofconcrete and designed for supporting electrical conductors servingnumerous purposes such as an electrical power transmission line or thelike and the invention more specifically pertains to a mast wherein aminimum of concrete is so disposed as to withstand forces in compressionat one side of the neutral axis and having prestressed tendons embeddedin portions of the concrete to handle the tensile stress developed atthe opposite side of the neutral axis.

The prior art includes poles formed of concrete reinforced with rods orthe like which are not prestressed but such structural elements have notbeen satisfactory. The principal deterrent to use of poles formed inaccordance with the teachings of the prior art is that they have been soheavy that they are diflicult to handle particularly when the length issuch as to satisfy present requirements of utility companies. It isaccordingly an object of this invention to provide a mast formed ofconcrete having tendons therein stresesd in tension with the concrete sodisposed and the tendons so located as to take advantage of thepronounced compression load resisting characteristics of the concreteand to make use of the pronounced tensile load carrying ability of steelor like tendons so as to obtain maximum benefit of these characteristicsand to dispose the tensile members at maximum distances from neutralaxes of the mast and at the sametime to reduce the bulk of the concrete.1

Another object of the invention is to provide a reinforced concrete mastfor supporting power lines or the like wherein the cross section of thepole is so shaped as.

to have a large perimeter surface to thereby increase con.- tact of theground with the mast structure to provide for improved anchorage of thepole in the earth.

A still further object of the invention is to provide a concrete mastwherein the cables are prestressed in tension and disposed in flangeslocated remotely of the geometrical center of the mast to therebyprovide large moment arms in relation to the neutral axis so that themast will be capable of handling laterally applied loads with a minimumof reinforcement and concrete.

Another object of the invention is to provide a mast formed of concreteand reinforcing elements which are prestressed in tension and so locatedwithin a particular cross section that the pole is capable ofwithstanding loads transversely of the electrical line and handlingloads applied longitudinally of the line.

Other objects and features of the invention will be appreciated andbecome apparent to those skilled in the masonry art pertaining tocantilever type structural elements and in the art pertaining to theelectrical line suspension systems as the'present disclosure proceedsand upon consideration of the accompanying drawing and the followingdetailed description wherein an exemplary embodiment of the invention isdisclosed.

In the drawing: I

Fig. 1- is'a 'side elevational view of a mast structure for supporting apower line wherein each of the upright members exhibits the invention.

Fig. 2 is an enlarged transverse sectional view of one of the uprightmembers taken on the line 22 of Fig. 1 with the bottom. webs omitted.

Fig. 3 is an enlarged transverse sectional view taken on the line 33 ofFig. 1.

The present invention is directed to a mast formed of plied near the topthereof and other masts exhibiting the invention of lesser or greaterheight will handle an equal load with the same factor of safety.

Referring to the drawing there is shown in Fig. 1 two masts 10 ofidentical construction which are often used in pairs as illustrated inassociation with a cross bar 11 for supporting a plurality of electricalconductors by means of insulator assemblies 12. When two masts areemployed angularly related members such as shown at 14 may be used andthe cross bar 11 is usually connected to the poles by means of braces16. The invention is directed to the structure of a mast 10 and thecharacteristics of one upright member is best shown in Figs. 2 and 3.

A mast embodying the invention includes a central web 18 which has amaximum width at the lower end of the upright member. The web 18 has athickness at the lower end of the mast which is substantially equal tothe thickness adjacent the upper end of the pole. The width of the web18 decreases in proceeding upwardly from the lower end of the pole aswill be apparent from a consideration of Figs. 2 and 3. The thickness ofthe web 18 however remains substantially uniform throughout the lengthof the pole. v

A web 21 is cast integral with one edge of the web 18 and the side web21 is arranged substantially transversely of the web 18. The side web 21has a thickness which remains substantially constant throughout thelength of the mast. The width of the side web 21 decreases inprogressing upwardly along the length of the mast. An outwardlyextending flange 26 and an outwardly extendting flange 27 is formedintegral with opposite ends of the side web 21. The cross sectionaldimensions of the flanges 26 and 27 adjacent the top of the mast aresubstantially the same as corresponding dimensions of the flanges at thebottom end of the mast. The flange portions 26 and 27 while havingsubstantially uniform cross sections throughout the length of the mastare progrcssively spaced closer to each other in proceeding from thebottom to the top of the mast.

A web 31 is provided at the opposite edge of the central web 18 and theside web 31 is arranged generally transversely of the web 18 and is castintegral therewith. The width of the side web 31 corresponds to that ofthe side web 21. The width of the web 31 progressively decreases inproceeding upwardly from the lower end of the pole so that the endadjacent the top of the mast has a dimension like that shown in Fig. 3.The thickness of the side web 31 remains substantially the samethroughout the length of the mast. A flange 32 is cast integral with oneend of the side web 31 and a flange 33 is formed integral with the otherend of the side web 31. The flanges 32 and 33 have the same transversedimensions throughout the length of the pole as will be apparent from aconsideration of Figs. 2 and 3. It will beobserved that large open areas30 are provided between the flanges 26 and 27 and between the flanges 32and 33.

The rate of decrease in the width of the central web 18 may vary and inone embodiment of a mast exhibit-.

ing the invention it has been found that the ratio of reduction of widthof this web in proceeding upwardly in order to provide for properstrength characteristics along the mast is at the rate of .021. The rateof reduction in the width of the side webs 21 and 31 may vary and in oneembodiment it has been found that a reduction in width at a ratio of.0116 has been found to be satisfactory to provide the proper strengthof the mast along its length.

The outwardly extending flange 26 has a plurality of prestressed tensionmembers or tendons which may take the form of steel or other cables 41.A plurality of prestressed tension members 42 are also provided in theoutwardly extending flange 27. It will be observed that these tendons 41are aligned with each other along the major dimension of each flange 26and the tension members 42 are similarly arranged in the flange 27.These tendons are each stressed lengthwise prior to the casting of theconcrete forming the mast and when the tensile members are of steel theyare each subjected to a prestressing of between 100,000 and 175,000pounds per square inch. After setting of the concrete there is some lossof prestressing in the tendons but suflicient tension is neverthelessmaintained in the cables to avoid the subjection of the concrete in theassociated portion or portions of the mast to tension stresses whenloads are applied laterally of the mast 10.

The flange 32 is provided with a plurality of prestressed tensionmembers or tendons which may also take the form of steel or other cables43. Similar tendons 4d are embedded in the flange portion 33. Thesetendons are stressed lengthwise prior to the casting of the concreteforming the mast and when the tensile members 43 and 44 are formed ofsteel each is subjected to a prestressing of between 100,000 and 175,000pounds per square inch. The tendons 43 are aligned with each otherlengthwise of the flange 32 and the tensile members 44 are similarlyarranged in the flange 33. The prestressing of the tensile members 43and 44 is such that during the application of forces to the poletransversely of the mast the concrete of the flanges 32 and 33 and inadjacent portions of the mast is not subjected to tensile stresses.

It will be observed that the outwardly extending flanges are widelyspaced in the lower portion of the mast and are joined to each other bya skeleton type structure which includes the side webs 21 and 31 joinedby the center Web 18. These webs have a small thickness in relation totheir width and the primary load handling portions of the mast are fourcorner or flange portions. Such a structure reduces the overall weightof the mast to provide a reinforced concrete mast capable of beingerected by conventional equipment and at the same time utilizes the bestcharacteristic features of the tendons and utilizes the ability ofconcrete to absorb forces in compression.

The center web 18 and the side webs 21 and 31 are of a thickness whichis sufficient to accommodate transverse tie members arranged at spacedintervals along the pole and one of such stirrups is shown at 51 in Fig.2 and another at 52 in Fig. 3. Another stirrup representing one of anumber arranged at spaced intervals along the mast is shown at 56 inFig. 2 and another is shown at 57 in Fig. 3. The side web 31 is providedwith stirrups at spaced intervals along the length of the pole and oneis shown at 58 in Fig. 2 and another at 59 in Fig. 3.

Additional longitudinally extending tendons 61 and 62 are provided andembedded in the concrete forming the mast. These tensile members may beformed of suitable material and in one embodiment take the form of steelcables. The tensile member 61 extends throughout the section of thecenter web 18 with the side web 21. The

tensile member 62 is arranged at the other edge of the center web 18 andis similarly located. When the tendons 61 and 62 are steel cables theyare each tensioned prior to casting of the concrete and are stressed intension between 100,000 and 175,000 pounds per square inch. The stirrups51 and 52 are desirably shaped so that the ends thereof embrace thetendons 61 and 62. Additional tendons 63 and 64 may be employed locatedin the side webs 21 and 31 and in portions thereof inwardly from theoutwardly extending flanges. When the tendons 63 and 64 are incorporatedthey are each prestressed prior to casting of the concrete by subjectingthem to loads in tension between 100,000 and 175,000 pounds per squareinch.

The cross sectional characteristics of the mast adjacent the lower endthereof as shown in Fig. 2 has an unusually large surface area measuredalong the perimeter of the pole. Thus when the lower end is planted inthe ground the level of which is indicated at 71 the earth contacts thepole over a large surface area. It is the practice to embed at least tenpercent of the pole so that all of the exterior surfaces of the polestructure frictionally contacts the earth to more firmly anchor themast. The flanges 27 and 33 may be joined by a horizontal web 72 whichis also formed integral with the side webs 21 and 31 and the central web18. A similar bottom web may be provided at the other side of the maststructure extending between the outwardly directed flanges 26 and 32 andintegral with the side webs 21 and 31 and the central web 18. Suchhorizontally disposed webs provide a base footing for the mast andpromote further good anchoring of the pole in the ground.

The side webs 21 and 31 while being arranged in planes generallytransverse of the central web 18 are not entirely within individualplanes. The slight outward bowing of the side webs provides a desirablefeature facilitating the removal of the forms after the concrete has setand this arrangement results in the disposition of the flanges furtherfrom the neutral axis of the mast.

While the invention has been described with reference to a concrete masthaving a particular cross sectional shape and provided with the tendonslocated in certain portions of the concrete it will be appreciated thatchanges may be made in the structural details and positions of thetensile members as well and the materials. Such modifications and othersmay be made without departing from the spirit and scope of the inventionas set forth in the appended claims.

What I claim and desire to secure by Letters Patent is:

1. A mast for supporting an electrical conductor in a position above theterrain comprising, a central web of solid concrete decreased in widthin proceeding upwardly along the mast and having a substantially uniformthickness throughout the length of the mast, a side web of solidconcrete with its intermediate portion integral with one edge of thecentral web and disposed in a plane generally transversely of saidcentral web, said side web decreasing in width in proceeding upwardlyalong the mast and having substantially a uniform thickness throughoutthe length of the mast, another side web of solid concrete with itsintermediate portion integral with the other edge of said central weband disposed in a plane generally transversely of the central web, saidsecond side web decreasing in width in proceeding upwardly along themast and having a substantially uniform thickness throughout the lengthof the mast, a flange of solid concrete integral with and extendingoutwardly from the outer face of each side web adjacent the free edgethereof, prestressed tendons within each flange extending throughout thelength of the mast, each of said flanges being of substantially uniformcross section throughout the length of the mast, and each flangeconverging towards each other flange in proceeding upwardly along themast.

portion integral with one edge of the central web and disposed in aplane generally transversely of said central web, said side webdecreasing in Width in proceeding upwardly along the mast and havingsubstantially a uniform thickness throughout the length of the mast,another side Web of solid concrete with its intermediate portionintegral with the other edge of said central web and disposed in a planegenerally transversely of the central web, said second side Webdecreasing in width in proceeding upwardly along the mast and having asubstantially uniform thickness throughout the length of the mast, anoutwardly extending flange of solid concrete integral with an outer freeedge of each side web, prestressed tendons within each flange extendingthroughout the length of the mast, each of said flanges being ofsubstantially uniform cross section throughout the length of the mast,and webs of solid concrete at a base of said mast formed integral withthe central web and said side webs and being disposed in a planesubstantially at right angles to the longitudinal axis of the mast withthe last-mentioned webs forming a base footing for the mast.

3. A mast for supporting a transmission line in an elevated positionabove the terrain comprising, a central web of solid concrete decreasingin width in proceeding upwardly along the mast at a rate ofapproximately .021 and having substantially a uniform thicknessthroughout the length of the mast, a side web of solid concrete havingits intermediate portion integral with one edge of said '6 central weband disposed in a plane generally transversely of the central web, saidside web having a substantially uniform thickness throughout the lengthof the mast with its width decreasing in proceeding upwardly along themast at a ratio of .0116, a second side web of solid concrete having itsintermediate portion integral with the other edge of the central web andbeing disposed in a plane generally transversely of said central web,said second side web having substantially a uniform thickness throughoutthe length of the mast with its width decreasing in proceeding upwardlyalong the mast at a ratio of .0116, a flange of solid concrete along andintegral with an outer face of the free edge of each side web,prestressed steel cables within each flange extending throughout thelength thereof with the tension of said cables prior to casting of theconcrete being between one hundred thousand and one hundred seventy-fivethousand pounds per square inch, and each of said flanges beingsubstantially of uniform cross section throughout the length of themast.

References Cited in the file of this patent UNITED STATES PATENTS1,071,045 Graa Aug. 26, 1913 FOREIGN PATENTS 518,279 France May 21, 1921804,429 France Aug. 3, 1936 449,668 Great Britain July 1, 1936 OTHERREFERENCES The Engineering nal, October 1953, pages 1235 -anr l1 2 86. i

